This invention relates to pneumatic core shafts and pneumatic shaft adapters, and in particular, to a system for directly monitoring operating criteria for pneumatic core shafts and pneumatic shaft adapters.
Pneumatic core shafts are expanding shafts for gripping and holding a core of a wound material roll. The shaft transmits torque to the roll of material from a motor, clutch or brake thereby winding, unwinding or stopping rotation of the core. The core shaft then engages and is driven by machine. The wound material can be any flexible web, e.g., paper, film, foil, nonwovens, and the like.
Pneumatic core shafts generally have a central air bladder or multiple air bladders within a bearing tube. Inflating the air bladder or bladders force attached lugs through openings in the bearing tube. A typical bladder will be pressurized to 80 psi. The lugs grip and hold the internal surface of the core of a web material roll. Lugs may have different shapes, such as ovals, buttons, strips, leafs, and spirals, Some pneumatic core shafts have multiple bladders such as with strip and leaf lugs,
Pneumatic shaft adapters typically enable the use of small diameter shafts with a larger diameter cores. One type of pneumatic shaft adapter has an external bladder, wherein the bladder expands to engage directly with the interior of a core. This same technology would be used on shaft adapters with a hollow central bore which slide over the outer diameter of another shaft to adapt from a smaller core size to a larger core size.
If air pressure in a core shaft or shaft adapter air bladder is lost during operation, the core can slip on the shaft or adapter, and torque is no longer transmitted from the motor, clutch or brake. This causes tension loss in the running web and results in process defects. Core slip can also damage the inside of the core so that a partially wound roll of material is no longer usable.
There is, therefore, a need to monitor air pressure in the shaft air bladder or pneumatic shaft adapter bladder to ensure no slipping is occurring. This is challenging due to the rotating nature of the shaft and core. Rotary unions are possible, but require complex pneumatic connections. There is also an advantage to automatically providing an alarm signal to a parent machine while running if a leak occurs. There is also an advantage to automatically providing a “ready to run” signal during air shaft or adapter inflation. With existing technologies, if an operator forgets to inflate, or only partially inflates, an unwind or rewind shaft, and then starts the machine, web material breaks are probable resulting in costly scrap as well as lost time to repair the operation. With larger shafts, the time to fill an air bladder to proper pressure may be up to ten minutes. An operator may believe a particular shaft or adapter is properly inflated, when it is actually underinflated. This leads to slippage and core damage.
Often times a slow leak in the bladder occurs before a large scale blow out. Detecting and alerting operators to a slow leak can prevent slippage and process mishaps. A slow leak is also indicative that maintenance needs to be performed on the shaft.
It is known to have variable air pressure inside a rewind shaft bladder. However, the air pressure sensing mechanisms is always located external to the shaft as part of the air supply line or integrated in an external air pressure transducer. These types of shafts are called “friction shafts” or “slip shafts” or “differential rewind shafts” and all require a constant air pressure connection be made through a rotary union to the shaft from a parent machine while the shaft is in operation.